Pierre Trudeau’s guiding motto in politics was “reason over passion.” In the end, it seems, he chose reason over life.

A newly released e-book from the Ottawa bureau chief for the Huffington Post reveals Trudeau refused treatment for advanced prostate cancer rather than face losing his famously sharp mind to dementia.

“At 80, Pierre Trudeau had been diagnosed with metastasized prostate cancer. His doctor had also told him he had early stages of dementia,” Althia Raj writes in Contender: The Justin Trudeau Story.

“The prostate cancer could be treated but the former prime minister wanted the cancer to claim him before he lost his mind.”

Justin Trudeau himself said he does not dispute the account, which suggests Trudeau made the decision about six months prior to his death in September 2000.

“The characterization in the book is certainly not something that I would say is false,” Trudeau — currently the prohibitive favourite to lead the party his father once helmed — said in a brief interview.

“It’s not anything that my father said explicitly to me. He may have said it to some other people,” he said.

“But for me, it was fairly clear that he was very much at peace with the end of his life approaching and certainly wasn’t interested in losing his quality of life, physically and mentally, and prolonging the process.

“He remained extremely lucid right up until the very end.”

Remaining lucid would doubtless have been a priority for Trudeau, a public intellectual before entering the political fray in the mid-1960s.

Dubbed a modern-day “Philosopher King,” Trudeau was acclaimed by his admirers as the most intelligent prime minister ever to preside over government in Canada.

He served as prime minister from 1968-1979 and, after a brief Joe Clark interregnum, again from 1980-84.

After declining treatment for cancer, Trudeau was able to spend the last six months of his life with his two sons, Justin and Alexandre. Justin, who had been teaching in Vancouver, moved back to Montreal to be with his father.

Trudeau died on Sept. 28, 2000.

His death sparked an outpouring of public mourning rarely seen in Canada.